Mannitol as a dry powder aerosol is used for bronchoprovocation testing and to enhance mucus
clearance in people with excessive airway secretions. The dose and distribution of the deposited
aerosol in the lung was investigated using fast single photon emission tomography
(SPECT) imaging. Mannitol powder (3 µm particle size) was produced by spray drying and
radiolabeled with 99mTc-DTPA. Approximately 60 mg of radiolabeled mannitol (containing
52–68 MBq of 99mTc-DTPA) was administered to 10 healthy subjects using the Inhalator™
dry powder inhaler (DPI), and SPECT images (1 min each) were collected. Thirteen percent
to 31% of the dose of mannitol loaded in the inhaler deposited in the lungs and the deposited
dose correlated positively with the peak inhalation air flow. The regional aerosol lung distribution,
as expressed by the penetration index (i.e., ratio of peripheral to central deposition
in the lung) varied from 0.31 to 0.88, which however showed no dependency on any flow parameters.
The variation in response to the same dose of mannitol within the asthmatic population
may in part be explained by these findings.
